Bot1320 Chapter 10 Plant Ecology
  1. Animals and plants undergo different sexual life cycles.
     
  2. Seed-bearing plants include Gymnosperms (conifers) and Angiosperms (flowering plants).
     
    • Angiosperms produce flowers for sexual reproduction.
      • • A sunflower, such as this cultivated Garden Sunflower has a composite inflorescence.

        In the center of the inflorescence is a cluster of disc florets; in the Garden Sunflower the disc florets produce seeds.

        On the outside is a cluster of ray florets; in the Cup Plant the ray florets produce seeds.

        The False Sunflower (Heliopsis helianthoides) can produce seeds from both disc and ray florets.

        Other composite plants include:

        • daisies (Ox-eye Daisy)
        • asters (Drummond's Aster)
        • goldenrods (Stiff Goldenrod)

       
    • After pollination, double fertilization yields a seed within the ovary.
       
    • The seed devlops into a fruit that protects and nourishes the embryo and also aids in seed dispersal.
     
  3. Plants grow at points called meristems.
    • Apical meristems initiate primary growth by cell division, producing primary xylem and primary phloem.

      Xylem and Phloem comprise a vascular system for transporting fluids.

      Xylem moves water and dissolved minerals from roots into the shoots.

      Phloem transports organic nutrients throughout the plant.


    • Continued growth yields 2 layers of cells: vascular cambium and cork cambium.

      Cell division within the vascular cambium forms secondary xylem (wood) and secondary phloem (inner bark).

      The cork cambium forms periderm (outer bark).

      The vascular cambium and cork cambium comprise the lateral meristem that spurs secondary growth.



    • Secondary xylem that develop in spring are relatively large and are known as early wood; those produced in summer or early fall are smaller and are known as late wood.
      Annual alternations between early wood and late wood are seen as growth rings in tree trunks.
     
  4. The above-ground stem may have flowers or leaves attached.
     
  5. Plant communities undergo ecological succession, interrupted by episodes of disturbance.
    • The diversity within a community is affected by levels of disturbance.

      In general, diversity is highest with a moderate (intermediate) level of disturbance.

      In a prairie community, fires that occur at an intermediate frequency (2-6 years) allow a mix of both early and late successional species, leading to greater diversity.